The DDS Crew have been breaking into London tube stations to paint trains for more than 20 years. Transport for London accuses them of causing £10m damage. Recently they have been filming themselves in the act. Now filmmakers Chris Atkins and Tom Oswald have gained access to their footage for a documentary, Underbelly. Here is an exclusive preview

A successful property surveyor was jailed this week after his secret life as a tagger was uncovered. But he wasn't unusual, says prolific train-writer Glynn Judd. Lots of us are middle-aged family men with good jobs